1. Field of the Invention
The present invention relates to an apparatus for measuring optical characteristic of an ablation standard object ablated with laser beam, an apparatus for measuring an ablation rate comprising the same, and an apparatus comprising either the former or the latter.
2. Description of Related Art
A well known processing apparatus ablates an object with laser beam. The processing apparatus ablates a corneal surface with excimer laser beam, thereby causing its curvature to change in order to correct ametropia of an eyeball.
When an excimer laser works successively under the condition that the fixed processing condition is given, an ablation depth per one shot, at the time of irradiating the same object to be processed, is considered approximately constant. (Where the ablation depth is referred to as "ablation rate", in the description, and one shot is referred to as "one scan" in the preferred embodiment.) However, the ablation rate often changes due to a kind of object to be processed, timing when the laser works, some factors such as output energy of the laser and the processing condition, and the like. The change of the ablation rate exerts a bad influence upon an apparatus such as to need accurate depth control, particularly upon an apparatus such as to ablate a cornea to form it into the desired and fixed shape. However, it is difficult to obtain an actual ablation rate of the cornea.
Therefore, the present applicant has been proposed an apparatus in U.S. Pat. No. 5,624,436 corresponding to Japanese Patent application laid-open No. HEI6(1994)-226471, by which the operator can easily obtain an ablation rate, the apparatus correcting based on the ablation rate. The apparatus disclosed in the publication ablates an ablation standard object having a known ablation rate (a transparent plate made from PMMA (polymethyl methacrylate)), where an ablation rate of an object (a cornea) is unknown, in order to form the ablation standard object into such a curved surface as to have the desired optical characteristic. Next, the operator measures the optical characteristic of the curved surface actually formed on the standard object with a measuring means (a lens_meter). The operator then inputs the measured data into the apparatus, then causing the apparatus to calculate the ablation rate of the object to be processed in a manner of comparing the desired optical characteristic with the actual optical characteristic, thereby correcting a driving information of the apparatus.
However, referring to above mentioned method, the operator causes the apparatus to ablate the standard object and then has to move the standard object from the ablation apparatus to a lens_meter commonly on sale in order to measure the object. It is troublesome for the operator and takes a lot of time. Accuracy of the measured results tend to be easily and subtly influenced by alignment of the standard object relative to a measuring optical system of the lens_meter and an operator's skill and knowledge for operating the same.
Further, in the case that the operator reads and inputs the results measured by the lens_meter into the ablation apparatus by using input means such as a keyboard and the like, there are possibility of artificial mistakes in reading and inputting the measured results. Input operation is also troublesome for the operator and takes a lot of time.